1. Field of the Invention
The present invention relates to an image forming method and image forming apparatus, which use a treatment liquid and a recording ink.
2. Description of the Related Art
Inkjet recording has widely used because of its advantages, such as low noise, and low running cost. Conventionally, dyes that have high solubility have been used for an ink of an inkjet printer to avoid clogging of the ink. In order to produce an image required to have water resistance and light fastness, such as a poster, however, an ink containing a pigment as a colorant has become more common.
When a color image is printed by an inkjet printer, moreover, in order to prevent blurring at an interface of different colors, such as an area where two colors are overlapped, penetration of an ink has been enhanced by adding a surfactant to the ink.
In accordance with the method for enhancing the penetration of the ink, bleeding can be prevented in a certain degree. However, the colorant penetrates deep into a recording medium together with the ink as a result of the enhanced penetration of the ink with respect to the recording medium, and therefore problems occur, such as low image density, and low color saturation.
Regarding the improvements of the inkjet recording method as mentioned above, known is an inkjet recording method using a treatment liquid having a function of aggregating the colorant contained in the ink.
For example, disclosed is a method for forming an image on a porous recording medium having excellent ink absorbency using an ink containing a self-dispersible pigment and a polyurethane binder, an ionic polymer precipitant or acidic precipitant (see Japanese Patent (JP-B) No. 4194531).
Moreover, disclosed is an image forming method, in which an inkjet ink containing an anionic dye or anionic compound and a pigment is aggregated using a liquid composition containing a cationic material and a nonionic high molecular material in combination to thereby prevent bleeding (see JP-B No. 3689444).
Moreover, disclosed is an image forming method, in which an ejected amount of an ink is reduced by using an ink for forming a secondary color in addition to inks of three colors, Y, M, and C in an ink set containing the inks and a reaction liquid that reacts with the inks, to thereby prevent creases of a recording medium (see JP-B No. 4448649).
Furthermore, disclosed is an image forming method, in which a high density image is formed without causing curling or cockling by using a treatment liquid containing a high concentration of a cationic high molecular material that reduces dispersibility of a recording ink containing an anionic colorant (see JP-B No. 4570118).
However, these image forming methods are used on an inkjet sheet or plain paper, which has excellent ink absorbency. If these methods are used on a recording medium of low absorbency, such as coated paper used for commercial printing, adjacent dots are joined together to cause beading, and transfer contamination, for example, to a conveying roller, is significantly caused as the recording medium is conveyed at high speed, such as in a line engine system.